This invention relates to a spring adjustment mechanism for a beater of a drum pedal enabling free adjustment of the beater amplitude and the pedal height and particularly to assuring that the tension on the return spring for the drum beater stays at a set level.
In a conventional beater mechanism for a bass drum, shown for example in FIGS. 9 and 10, supports 92 are erected at both sides of the base 91 of a drum pedal device 90. A beater rotary shaft 94 is freely rotatably supported at the tops of the supports 92 through respective ball bearings 93.
There is a beater 110 approximately at the center of the rotary shaft 94, and next to the beater is an operating member 120, which is in the shape of a wheel or sprocket. Both rotate integrally with the beater 110. The beater head 115 is fixed to the beater 110 by means of stopping screws 116.
The operating member 120 comprises a sprocket or a partial sprocket, with a chain 121 having an end that is fixed at the operating member 120 and is wound on its outer periphery. The other end of the chain 121 is linked to the tip of a foot pedal 95. As the foot pedal 95 is stepped on, as indicated by an arrow mark A in FIG. 9, the chain 121 is pulled down. This rotates the operating member 120 which in turn rotates the beater, thereby causing the beater head 115 to beat the drum head surface D.
A cam 100 is fixed at the end of the rotary shaft 94 by a stopper screw 101, as shown in FIG. 11. The cam 100 has the approximate shape of a fan, as shown in FIG. 9. At that position which corresponds to the pivot of the fan, there is a shaft receiving hole 102 through which the rotary shaft 94 is installed. A plurality of roller installation holes 103 may be provided spaced away from the hole 102 at various positions over the cam.
A roller installation bolt 104 is screwed into one of the roller installation holes 103 which is selected dependent upon the initial pivot orientation of the cam 100. A hanging ring 106 is suspended from a roller 105 that is installed on the roller installation bolt 104. The top end of a tension spring 107 is engaged at the bottom tip of the hanging ring 106. The bottom end of the spring 107 is engaged with a lower bracket 109 at the outside of the support 92. The spring 107 is tensioned to normally return the beater 115 to its original position automatically. An adjustment bolt 108 adjusts the tension of the spring 107. A clamp 130 holds the beater mechanism to the drum hoop.
Adjustment of the tension of the spring 107 in the above conventional device is done with an adjustment device 140 which is provided at the bottom of the spring 107. The adjustment device 140 comprises an adjustment screw 141, an adjustment nut 142 threaded on the screw below the bracket 109 and a lock nut 143 threaded on the screw above the bracket 109. The adjustment screw 141 is inserted through an adjustment screw insertion hole 144 in the lower bracket 109 and is linked to the lower end of the spring 107. The screw is then secured from below the lower bracket 109 by the adjusting nut 142 and is locked in the selected adjusted position by tightening the lock nut 143 against the bracket 109. A metal washer 145 seats the lock nut 143 firmly.
For adjusting the tension of the spring 107, the lock nut 143 is loosened, and the adjusting nut 142 is rotated until the spring 107 has a desired spring tension. Then the lock nut 143 is tightened against the lower bracket 109, thereby fixing the position of the adjustment screw 141.
In the above described mechanism of the prior art, however, during rotation of the adjustment nut 142, the adjustment screw 141 may also rotate inside the installation hole 144 of the lower bracket 109, thereby changing the direction of the screw. This also changes the direction of the spring 107 causing a delicate change in the resistance, or load or tension of the spring due to its being twisted.
In addition, it is believed that the resistance by the adjustment screw serves as one cause of early weakening of the tensile strength of the spring 107. During use of the drum pedal, further, the adjustment nut 142 may become loosened so that the adjustment screw 141 becomes shaky, with a possibility that the set position of the desired spring tension may change.
Moreover, there is resistance to adjustment of the tension in the spring due to the friction between the roller 105 and the installation part 104. This resistance also delicately affects the amplitude of the beater.